如何使用Javascript将数组vlaue从函数中传递出去

Question

I am an absolute JavaScript newbie, however I am working on a private Project. In a nutshell I will be reading a few flat files (.csv/.txt format) and passing the values to HighCharts.

I have a handle on nearly everything (I think).

The only bit I can't get is reading the files into an array, then picking the bits out I need. I can use a script to pass the files straight into Highcharts, but it's not flexible enough for what I need.

Anyway for the below Livedata.txt contains

1370576580,Acidity,pH,8.20,ORP,mV,366.99,ReefTemp,DegC,25.1,RoomTemp,DegC,21.7,HeaterTemp,DegC,25.1

(EPOCH, then groups of 3 data points (measure, unit, value) for 5 probes)

My (the snippet of my) script is:

---

var $livedata = new Array();
var currentph;
$.get('livedata.txt', function(data){
        livedata = data.split(',');
});
currentph = $livedata[3];
document.write("<b>currentph is </b>=>"+currentph+"<br>");

---

like this the var currentph = undefined

If I move the document.write statement into the $.get (is this a function?) it does contain the value 8.20

Furthermore if I declare currentph as 8.20 the rest of my script accepts this value fine.

Any help/suggestions are much appreciated.

I will be declaring 16 variables, 1 for each value in the array (just for the sake of reading the script later).

Cheers

Answer 1

Because the $.get is asyn. When you call currentph = $livedata[3]; right after that, the response does not arrive yet. That's the reason why it works when you move the document.write statement into the $.get 's callback function. Also check your typo, you're missing $ before livedata . If you need to do syn call, you can try $.ajax with async:false

$.ajax(
     {
       url:'livedata.txt', 
       async:false,
       success: function(data){
         $livedata = data.split(',');
       }
    }
);

Answer 2

1. You forgot to prefix $ to your variable livedata .
2. Other issues with your code are that; a) If 'livedata.txt' is never loaded, $livedata would be an empty array; b) If 'livedata.txt' is loaded, but does not have at least 4 comma separated values, the $livedata[3] would be undefined.

You may want to re-write your code with something like this:

var $livedata = []; // array literal notation

$.get('livedata.txt', function(data){
        $livedata = data.split(',');
});

// in case array does not have an index 3, set value to 'not found'
var currentph = $livedata[3] || 'not found';

document.write("<b>currentph is </b>=>"+currentph+"<br>");